1. Field of the Invention
This invention relates to electrochemical cells containing liquid sodium as the anodic material.
2. Prior Art
In sodium sulphur cells, liquid sodium forming the anodic material is separated by a solid electrolyte, usually of beta alumina, from the cathodic reactant comprising sulphur/sodium polysulphides. The anodic and cathodic materials, if allowed to mix, as would occur if the electrolyte was breached, react exothermically and for this reason it is the practice, in such cells, to maintain only a small quantity of sodium over the anodic surface of the electrolyte element, gas pressure and/or a capillary or wicking system being used to force or draw up sodium from a reservoir into the anodic region adjacent the electrolyte. In a tubular cell, the anodic region is an annular region between one surface of the electrolyte tube and an anode current collector; the sodium may be inside or outside the electrolyte tube. Very conveniently however the anode current collector is a metal housing surrounding the electrolyte tube and the sodium is in the annular region between this housing and the electrolyte tube. To constitute a wicking medium and to reduce the quantity of sodium in this annular region, it is a common practice to fill the region with carbon powder or small glass beads or alumina, these materials being chemically and electrochemically inert with respect to the sodium and the electrolyte material. See for example U.S. Pat. No. 4,048,391.